Sorry, this is a long one.

Elroy posted in a recent thread his observations about one of his Yamaha CD player sounding better than his Marantz when they were used as transports feeding his Zhaolu DAC. A significant group of other members agreed that transport quality does make a difference when using an external DAC. As a counterpoint one of the more recent threads I started discussed exactly the opposing position, that transport quality was almost irrelevant. Similarly my position on the matter also had its supporters. I wanted to get to the bottom of this, so I have done some more research on the topic and read a good ARTICLE on Stereophile that helped me understand why we BOTH might be correct.

The article discusses jitter, including what it is, where it comes from, and how it can be minimized. Based on this article it seems that the following is necessary for a low-jitter clock and best possible D-to-A conversion by the DAC...

1. A low-jitter signal transmitted from the transport.

"Although a low-jitter transmitter and interface isn't, in theory, that difficult to design, bad cables and transmitters/transports abound in the real world... it is easier to build a low-jitter transmitter than a low-jitter receiver. There is no excuse for designing a jittery transport."

2. Proper impedance match between transmitter, cable and receiver.

"A 10' cable represents a round-trip delay of about 30ns (30,000ps), and any impedance mismatch adds an attenuated echo signal with the same 30ns delay... A tolerance of 5% is a good starting point; 3% would be better. The consumer S/PDIF interface, with a 75-ohm ±5% impedance spec, is probably acceptable... Once the transmitter/transport and the receiver have the proper impedance, the cable needs to be impedance-matched."

3. A well shielded, low noise cable.

"Jitter has multiple causes. One of them is electrical noise picked up on the interface cable. Noise causes the zero crossing points to shift slightly—which is, by definition, interface jitter. If the digital interface signal has an average slope of 20V/µs (a typical value in many S/PDIF implementations), just 10mV RMS of noise, for example, will introduce 500ps RMS of jitter."

4. A well designed input receiver in the digital processor.

"Barring design and layout errors, the jitter performance of a digital processor is primarily dependent on the input receiver stage... the receiver is, at least conceptually, clearly the most difficult one to design and manufacture... A more significant appraisal of input-receiver performance, however, is how well it rejects jitter in the incoming signal. Does the input receiver pass jitter from the transport to the recovered clock, or does it attenuate it?... The jitter in the recovered clock (what we're really concerned about) is thus a function of the transport's jitter, the interface-induced jitter, the input receiver's ability to reject incoming jitter, and the input receiver's intrinsic jitter."

This idea of jitter rejection is what got me re-thinking my observations, where I found the transport to be mostly irrelevant to the quality of sound output from a separate DAC. A DAC's input receiver uses a phase-locked loop (PLL). The article discusses that... "By their nature, PLLs reject incoming jitter only above a certain frequency, called the jitter attenuation cutoff frequency. Consequently, we must consider both the receiver's intrinsic jitter and its jitter attenuation cutoff frequency when specifying an input receiver's performance. The single intrinsic jitter specification doesn't tell the whole story." So it seems that a quality input receiver can eliminate a significant portion of jitter that may originate from a poor transport and cabling. If that input receiver adds only a minimum of jitter itself, the resulting clock will be much more accurate and support the most accurate reproduction of music by the DAC.

The article then compares a few of the best input receivers at that time (1993)... "The best currently available monolithic (chip) input receiver is the Crystal CS8412. This has an intrinsic jitter of 200ps and a jitter attenuation cutoff frequency of 25kHz. With no input signal, the CS8412 will introduce 200ps of clock jitter. Jitter in the incoming data stream with a frequency below 25kHz will be passed to the recovered clock. The performance achieved by the best currently available hybrid digital audio receiver (UltraAnalog AES 20) is typically 40ps for intrinsic jitter and 1kHz for jitter attenuation cutoff frequency." I also checked online for the more recent CS8414 and CS8416 and found that they have the same 200ps of intrinsic jitter, although a somewhat better jitter attenuation cutoff frequency (10kHz for the CS8416). Also for comparison I looked up the Burr Brown DIR1701. It has 80ps of intrinsic jitter and 9.5kHz jitter attenuation cutoff frequency.

The older UltraAnalog AES 20 seems to be superior to even the more current Cirrus/Crystal and Burr Brown input receivers, in both specifications. When Stereophile reviewed the Sonic Frontiers SFD-2 DAC ($4695 in 1993) they wrote this about the UltraAnalog AES 20...

"The SFD-2 is the first product to use UltraAnalog's AES20 input receiver, a sophisticated module that replaces the Crystal CS8412 or Yamaha YM3623 chip. Unlike these two purely monolithic chips, the AES20 is a combination of monolithic and discrete devices encapsulated in a potted module measuring 1.5" by 2". The AES20—which spent more than a year in development—greatly reduces jitter in the digital processor in which it is used.

The AES20 does this in two ways. First, it has very low intrinsic jitter, meaning that the AES20 adds very little jitter of its own to the clock recovered from the incoming digital datastream. According to the spec sheet, the AES20 has less than 40ps of intrinsic jitter, one fifth the Crystal CS8412's intrinsic jitter (specified at 200ps), and orders of magnitude less jitter than the Yamaha YM3623. Second, the AES20 rejects jitter in the incoming datastream from a CD transport instead of passing the jitter to the recovered clock. The frequency at which an input receiver begins to reject incoming jitter is called its "jitter attenuation cutoff frequency" (JACF). The Crystal CS8412's JACF is specified at 25kHz, meaning that jitter below 25kHz will be passed to the recovered clock, and jitter above 25kHz will be attenuated. The AES20's JACF is 1kHz, meaning that transport jitter above this frequency will be attenuated. Note that jitter from 0-40kHz causes audible problems (in multi-bit DACs)."

I did some research online and discovered that the Zhaolu DAC uses the CS8416 input receiver (I could find no info on the EAD DSP-1000). Like the Sonic Frontiers SFD-2, my PS Audio Ultralink Two uses the UltraAnalog AES 20 (and also the same UltraAnalog DACs). I suspect that this may explain why I perceive little difference between transports, and other here on the forum do. Since the UltraAnalog AES 20 has a very good JACF it rejects far more jitter originating from the transport and cabling, resulting in a greater immunity to deficiencies within the source digital signal. Without this ability to reject source jitter, the Zhaolu DAC (and I suspect the EAD DSP-1000) is much more sensitive to the quality of the input signal, including transport and cabling.

With this knowledge I think I can now jump on the bandwagon of those that say that transports can sound different, even through the same DAC. However, I would add that the degree to which those differences are relevant depends greatly on the ability of the DAC's digital input receiver to attenuate source jitter.

I hope you all found this informative and relevant.

Rob

dingus has a $200 coax cable that I am going to use on the older maranzt, and I will use my $7.99 optical on the yamaha, and see if that evens up the score a bit.

very interesting read, I didnt understand too much of the numbers and electronic stuff. but some of it made sense.

elroy

Yeah, I guess it does sound a bit confusing. Basically the idea is that some input circuits are better at ignoring "junk" within the digital signal than others. The better your DAC's input circuit can ignore the "junk", the less sensitive it will be to poor quality transports and cabling.

I realize that I am essentially saying that the reason that I don't hear a real difference between various transports, and that you do, is because my DAC is better than yours. So I hope that doesn't come across the wrong way. I was actually just really happy to finally understand why the supposedly obvious differences between transports were never apparent to me in the past.

This also helped me better understand why my PS Audio Ultralink Two retailed for $2295 when new, and why it was rated Class B in Stereophile's "Recommended Components" as recently as April 1997.

Rob

... so going by the article it would seem that anything which reduces jitter in the chain may yield better sound. if i got that right then any part of the chain (transport/signal transmitter, cable, input receiver/DAC) can make a difference for the good or bad.

Yes they can affect the jitter performance.

I know pretty well what jitter is and i'd post a few posts about it at ST so, here's a couple more - http://www.troisi.com/lit/jitter.PDF and http://www.positive-feedback.com/Issue43/jitter.htm but the questions i'd made in the past were:

- Does someone can hear jitter?
- If not, does it matters?

WHAT!!!!! NO WAY!!!! my $200 dac should compete, dang I hate losing ,

Now it makes more sense, basically, inexpensive gear can let you hear more problems with the sound, ergo, less clear, and defined, blah,blah,blah, right.

So if I had a 3K DAC, it would filter out more of the jitter anomaly's and the transport wouldnt make much difference, that is probably why I didnt hear hardly any difference in sound at dingus's when we A/B'd between the wadia and the Kenwood.

elroy

hear is my thought on jitter,

Jitter is all those things that Rob was saying in his super long post, all the crap, and extraneous noise, so Ya I guess you can hear jitter, because your stereo doesnt sound as good as it could. If I was able to get rob's DAC, and Cables, It seems that I could use any transport, and not lose sound quality.

so I think, bad sound might be what I think jitter is now.

elroy

No. It means the Kenwood is also a very good transport.

O,

I don't think you have to spend that much money. On the used market the Adcom GDA-700 uses the UltraAnalog AES 21 input receiver, with its excellent jitter rejection. The GDA-700 can be found used in the $250-350 range. If you insist on new gear, I stumbled across the Niko Audio D100, which uses the Wolfson WM8804 input receiver. The intrinsic jitter and jitter rejection specs of this circuit make the excellent UltraAnalog circuits look like crap. I would love to give this DAC a listen. It sounds like it has all of the right pieces to be a true high-end component, and would be a relative bargain for $1295 (MSRP).

Yep this true. However, if the input receiver in your DAC is good at rejecting jitter, you have some immunity to problems further up the chain. If in addition to that it has low intrinsic jitter, the overall jitter seen at the DAC will be very low in most cases.

I can't really say, because as I mentioned I couldn't find any info on which input receiver that the EAD DSP-1000 uses. Either the EAD uses a really good input receiver, or the Kenwood is a pretty good transport with good transmission circuits. Maybe dingus would be willing to crack open his DAC and try to figure out which input receiver it uses.

Ok, I can be a little thick once in a while,

Before I got the Yamaha, I ran the Marantz, 67se and a 1/2 pound panasonic dvd/cd/mp3/whatever player, basically a 50$ player, and I ran them through my DAC and I couldnt hear any difference in sound. From what I have heard, the Marantz is decently regarded as a cd player, it is fairly heavy and stable, and decent build quality. so what I get out of it, is that the sound improvement was the Transport. and only the transport.

elroy

ok I wrote that stuff above a minute ago, and re-read some of the posts, So Crap begets Crap, in a nutshell. and now I am a thick genius

did that a while back, clint made the necessary interpretation...
http://www.sound-thinking.org/index.php?sh...indpost&p=43398

yes the Kenwood made for a very nice transport for redbook cd's. oddly enough it was rather poor as a stand alone player in this capacity.

So it uses the CS8412 which as the Stereophile article says was considered the best monolithic (chip) input receiver in the early 90's, but was behind the best hybrid input receiver of the time, the UltraAnalog AES 20.

This further confirms to me the different observations that have been reported when evaluating various components as transports.

Regarding the Kenwood... now knowing that the EAD DAC uses the CS8412, I would say that the Kenwood's good results indicate it is a pretty good transport. Its poor performance as a stand-alone player is likely due to deficiencies in its internal DAC or analog section.